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United States Patent | 5,519,317 |
Guichard ,   et al. | May 21, 1996 |
An inductive proximity sensor has a resonant circuit including a sensing coil and driven by an oscillator at a predetermined frequency. To sense selectively ferrous and non-ferrous objects, the excitation frequency is a subcritical excitation frequency and discriminator logic is provided to process a phase-shift signal and a damping signal.
Inventors: | Guichard; Christophe (Angouleme, FR); Leonard; Didier (Moulidars, FR) |
Assignee: | Schneider Electric SA (Boulogne-Billancourt, FR) |
Appl. No.: | 397956 |
Filed: | March 3, 1995 |
Mar 04, 1994[FR] | 94 02623 |
Current U.S. Class: | 324/236; 324/327; 324/334; 331/65 |
Intern'l Class: | G01N 027/00; G01V 003/10; H03K 017/95 |
Field of Search: | 324/327,328,332,333,207.16,207.26,233,234,236-238 331/65 361/180 307/116,117 |
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3826973 | Jul., 1974 | Pflaum | 324/233. |
3896371 | Jul., 1975 | Hametta | 324/327. |
4473799 | Sep., 1984 | Favre | 324/236. |
4879531 | Nov., 1989 | Tigges et al. | 324/327. |
Foreign Patent Documents | |||
0393359A2 | Oct., 1990 | EP. | |
0399563A2 | Nov., 1990 | EP. | |
4212363A1 | Oct., 1993 | DE. | |
2158583 | Nov., 1985 | GB. | |
EP0222805 | Nov., 1986 | WO. |